A gas turbine (GT) exhaust diffuser is a divergent annular flow path between inner and outer annular diffuser shells through which the exhaust gas passes. The cross-sectional area of the duct progressively increases in the flow direction to reduce the speed of the exhaust flow and increase its pressure. The exhaust diffuser is commonly fabricated in an upper and lower halves joined along horizontal joints between the inner and outer shells. The diffuser halves require complex fabrication, including complex machining profiles along the horizontal joints. There is potential for misalignment between the upper and lower halves, especially radial misalignment, which can make alignment of bolt holes for joining difficult.
The diffuser may operate at temperatures of 500-700° C. or more, and experiences thermal and mechanical stresses due to operational gradients and GT start/shutdown cycles. This results in material distortions that make it difficult to realign the halves of the diffuser after manufacturing, transport, and disassembly for servicing purposes.